The mechanism, role and control of the inactivation of glutamate dehydrogenases in yeast.

GDH* occupies a central role in the metabolism of many microorganisms because it provides a link betweeen carbohydrate and nitrogen metabolism (Smith et al., 1975; Brown et al., 1974). Many simple eukaryotic micro-organisms possess two genetically distinct forms of GDH with different nucleotide specificities, a catabolic role being assigned to the NAD-specific enzyme, whereas the NADP-specific enzyme performs an anabolic function (Smith et al., 1975; Brown et al., 1974). Originally it was thought that the concurrent regulation of glutamate biosynthesis and degradation was achieved by rigorous control of the synthesis of NAD-GDH and NADPGDH under different growth conditions (Stachow & Sanwal. 1967). It is now apparent that additional control mechanisms operate to regulate the activity of NAF-GDH and NADP-GDH (Hemmings, 1978a, b). This article discusses the role of protein phosphorylation in the regulation of NAD-GDH, and the role of specific enzyme degradation in regulating the activity of NADP-GDH.